This invention relates to methods for producing silicon nitride films and silicon oxynitride films. More particularly, this invention relates to methods for producing silicon nitride films and silicon oxynitride films by thermal chemical vapor deposition (thermal CVD).
Silicon nitride films have excellent barrier properties and an excellent oxidation resistance and as a consequence are used in the fabrication of semiconductor devices, for example, as an etch-stop layer, barrier layer, or gate dielectric layer, and in oxide/nitride stacks.
Plasma-enhanced CVD (PECVD) and low-pressure CVD (LPCVD) are the methods primarily used at the present time to form silicon nitride films.
PECVD is typically carried out by introducing a silicon source (typically silane) and a nitrogen source (typically ammonia, but more recently nitrogen) between a pair of parallel plate electrodes and applying high-frequency energy across the electrodes at low temperatures (about 300° C.) and low pressures (1 mtorr to 1 torr) in order to induce the generation of a plasma from the silicon source and nitrogen source. The active silicon species and active nitrogen species in the resulting plasma react with each other to produce a silicon nitride film. The silicon nitride films formed in this manner by PECVD typically do not have a stoichiometric composition and are also hydrogen rich and accordingly exhibit a low film density, a poor step coverage, a fast etching rate, and a poor thermal stability.
LPCVD uses low pressures (0.1 to 2 torr) and high temperatures (700° C. to 900° C.) and produces silicon nitride films with a quality superior to that of the silicon nitride films produced by PECVD. At the present time silicon nitride is typically produced by LPCVD by the reaction of dichlorosilane and gaseous ammonia. However, ammonium chloride is produced as a by-product in the reaction of dichlorosilane and gaseous ammonia in this LPCVD procedure: this ammonium chloride accumulates in and clogs the reactor exhaust lines and also deposits on the wafer.
Methods using chlorine-free silicon nitride precursors, i.e., alkylsilanes, aminosilanes, have been proposed in order to solve the aforementioned problems. All of these precursors, however, contain carbon. In accordance with the present invention, the inventors have discovered that the use of these precursors, either alone or in combination with ammonia, results in the incorporation of silicon carbide and/or free carbon in the resulting silicon nitride film and a deterioration in the insulating characteristics of this film.
This problem also occurs when the aforementioned prior art precursors are used to produce silicon oxynitride films (with the same precursors, nitrogen containing gases plus an oxygen containing gas, which are films that have the same properties and applications as silicon nitride films.
The formation of silicon nitride on a silicon oxide film by the reaction of ammonia and trisilylamine (TSA) at 720–740° C. and an ammonia (TSA partial pressure ratio of 5:1; TSA partial pressure=5×10−2 torr) has been reported very recently (M. Copel et al., Applied Physics Letters, Vol. 74, Number 13, 1999). However, this article does not go beyond reporting on the silicon nitride growth mechanism, nor does it provide any evaluation of the properties of the produced silicon nitride films. Moreover, this article is silent on the formation of silicon oxynitride films using TSA.
Accordingly, there is a need to day to provide a CVD-based method that can produce silicon nitride films and silicon oxynitride films with improved film characteristics without the accompanying generation of ammonium chloride and without incorporation of carbonaceous contaminants into the films.